Discuss Three Phase overhead supply is it TN C in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

Michael J

Michael J
Messages
97
Location
Swansea
While carrying out a EICR I found on first inspection that there were no RCDs installed . When I checked at the Pole Mounted Transformer the Earth & Neutral were connected at the Neutral point. So am I right in concluding it's a TN-C System? The 17th Edition states that RCDs should not be installed where a TN C System is used (411.4.4)
 

buzzlightyear

please let me back in to the prison cell.
Electrician's Arms
Messages
6,982
Location
star command
Are you sure it is tncs on the pole or TT.what is in the property?.
got any pic of the board .
 
OP
Michael J

Michael J

Michael J
Messages
97
Location
Swansea
I will take a pic tomorrow,but it looks like the Earth and Neutral are connected at the transfer. The reason I am suspecting is a TN-C is the lack of RCD protection on the Ring main final circuits. If it was a TT it would be protected with RCD at the mains
 
OP
Michael J

Michael J

Michael J
Messages
97
Location
Swansea
Yes, or any final circuit in the building, by the way it feeds a hotel. The overhead feed is by way of bundle conductors (4) sorry that's a South African term. I don't know what you call them here?
 

Archy Styrigg

Mentor
Electrician's Arms
Trainee Access
Messages
10,143
Location
Manchester
Eh?
The 17th Edition states that RCDs should not be installed where a TN C System is used 411.4.4

The following types of protective device may be used for fault protection:
(i) An overcurrent protective device
(ii) An RCD.

It'll be a PME supply. Concentric cable split at the installation intake, to N & E.
 
OP
Michael J

Michael J

Michael J
Messages
97
Location
Swansea
Eh?
The 17th Edition states that RCDs should not be installed where a TN C System is used 411.4.4

The following types of protective device may be used for fault protection:
(i) An overcurrent protective device
(ii) An RCD.

It'll be a PME supply. Concentric cable split at the installation intake, to N & E.
Read on a couple of lines after Note 1
"An RCD Shat be used in a TN-C system"
 

Strima

Electrician's Arms
Messages
3,630
Location
St Neots
That'll be 414.4.5 for no RCD on TN-C?
 

buzzlightyear

please let me back in to the prison cell.
Electrician's Arms
Messages
6,982
Location
star command
Strima are you not counting sheep in your bed .LoL .because im in night garden with iggle piggle.;)
 
OP
Michael J

Michael J

Michael J
Messages
97
Location
Swansea
I think you might be getting confused here chief, TNC is NOT allowed within an installation. TNC/PME supply, then the Earth is split off at the intake.
Thanks, I will take a closer look at the intake, I just don't understand why there are no RCDs on the final ring circuits this hotel has 6 DBs
 

darkwood

Super Moderator
Staff member
Super Moderator
Moderator
Mentor
Electrician's Arms
Trainee Access
Messages
13,280
Location
West Yorkshire
My house has a two wire supply coming in along the outside wall, it was clearly a TT in the past but has been converted to TNC even though the supply is via 2 individual separate single cores.
The DNO risk access any existing TT before conversion I am led to believe, I see no reason why your install won't have been converted at some point even an overhead supply.
 

Strima

Electrician's Arms
Messages
3,630
Location
St Neots
Strima are you not counting sheep in your bed .LoL .because im in night garden with iggle piggle.;)
A people said the Magic Roundabout was messed up...
 

westward10

In echoed steps I walk across an empty dream.
Staff member
Moderator
Mentor
Electrician's Arms
Trainee Access
Messages
11,942
Location
Northamptonshire
You probably have TN-C external to the building then the PEN conductor is separated at the service head which gives the S on TN-C-S.
 

davesparks

Mentor
Electrician's Arms
Trainee Access
Messages
13,305
Location
guildford
While carrying out a EICR I found on first inspection that there were no RCDs installed . When I checked at the Pole Mounted Transformer the Earth & Neutral were connected at the Neutral point. So am I right in concluding it's a TN-C System? The 17th Edition states that RCDs should not be installed where a TN C System is used (411.4.4)
Far more likely to be a PNB supply which is a form of TNCS.

A lack of RCDs does not dictate what the supply type is, its either a sign of the age of the installation or of non compliant work.
 

Permanent unswitched live colour?

  • Brown

    Votes: 60 66.7%
  • Black

    Votes: 30 33.3%

Electrician Talk

Top